The invention relates to a method for checking the functional capacity of an exhaust gas recycling system on an internal combustion engine.
Exhaust gas recycling systems are used to reduce the proportion of nitrogen oxide in the exhaust gas of an internal combustion engine. A proportion of the exhaust gas is returned via an exhaust gas recycling line from the exhaust gas tract into the inlet tract, i.e. into the collector in the manifold pipe. Electrical signals from a control device are used to activate an exhaust gas recycling valve in the exhaust gas recycling line, thereby adjusting the mass of the recycled exhaust gas. As the basic components of the exhaust gas in the internal combustion engine mean that it is an inert gas, adding exhaust gas to the combustion air intake can reduce the peak combustion temperature and thereby reduce the emission of nitrogen oxides. The mass of the recycled exhaust gas in relation to the sum of the mass of the fresh gas (air intake) and the mass of recycled exhaust gas is generally designated as the exhaust gas recycling rate.
Monitoring of the capacity of such an exhaust gas recycling valve to be controlled and closed is essential in order to be able to ensure its correct operation. In order to comply with the exhaust gas limit values required by legislation, it is necessary to equip vehicles with diagnostic equipment which makes it possible to detect malfunctions of sensors and systems associated with the control or activation of components relating to the exhaust gas and to issue appropriate error messages. The checking of all components in the air route is of particular significance with regard to compliance with the statutory guidelines for on board diagnosis (OBD) for vehicles. In particular it must be possible for the exhaust gas recycling valve to close completely, as otherwise, if the internal combustion engine operates with the exhaust gas recycling valve constantly open, the required exhaust gas limit values may be exceeded.
An abnormality detection method and a device for an exhaust gas recycling control system on an internal combustion engine are disclosed in DE 195 27 030 A1. The abnormality here is the result of operational delay on the part of a diaphragm, which forms an exhaust gas recycling valve (EGR valve). The exhaust gas recycling valve is controlled on the basis of engine operating data and intake distributor pressure. A condition which has to be fulfilled to activate the abnormality decision is detected. On detection of the abnormality decision activation condition the exhaust gas recycling valve is forcibly opened or closed. Depending on the difference in intake distributor pressure on forcible opening/closing of the exhaust gas recycling valve, a possible abnormality of the exhaust gas recycling valve is concluded.
The object of the invention is to specify a method which can be used to check the functional capacity of the exhaust gas recycling system on the internal combustion engine simply and without additional sensors during operation of the internal combustion engine and without adversely affecting the driving operation. This object can be achieved by a method for checking the functional capacity of an exhaust gas recycling system on an internal combustion engine comprising the steps of:
providing an exhaust gas recycling line, which connects an exhaust gas tract on the internal combustion engine to an inlet tract on the internal combustion engine, so that exhaust gas can be returned to the inlet tract,
providing an exhaust gas recycling valve located in the exhaust gas recycling line used to adjust the traversable cross-section of the exhaust gas recycling line and activated by electrical signals,
activating the exhaust gas recycling activated for diagnosis purposes such that operating parameters of the internal combustion engine change and the reaction of the operating parameters is analysed, wherein when the internal combustion engine is in the idle state and the vehicle driven by the internal combustion engine is stationary, using the output signal of an airflow detector located in the inlet tract upstream from the junction with the exhaust gas recycling line as the operating parameter.
The activation signal for the exhaust gas recycling valve can be set to zero based on a value set in the idle state, in order to close the exhaust gas recycling valve. After expiry of a predefined first time period the signal from the airflow detector can be detected and compared with a first threshold value. It can be concluded that the exhaust gas recycling valve is faulty with regard to dynamic behaviour, if the threshold value is not exceeded within the first time period. The activation signal for the exhaust gas recycling valve can also be set to zero on the basis of a value set in the idle state, in order to close the exhaust gas recycling valve, after expiry of a predefined second time period the signal from the airflow detector can be detected and compared with a second threshold value and it can be concluded that the exhaust gas recycling valve is faulty with regard to its capacity to close completely, if the threshold value is not exceeded within the second time period. On identification of a faulty exhaust gas recycling valve, a corresponding entry can be made in an error memory. The check can be terminated if the engine is no longer in the idle state or the vehicle is no longer stationary within a predefined time period. The threshold values and the time periods can be determined by experiment and stored in a memory device.
An arrangement for checking the functional capacity of an exhaust gas recycling system on an internal combustion engine, comprises:
an exhaust gas recycling line, which connects an exhaust gas tract on the internal combustion engine to an inlet tract on the internal combustion engine, so that exhaust gas can be returned to the inlet tract,
an exhaust gas recycling valve located in the exhaust gas recycling line used to adjust the traversable cross-section of the exhaust gas recycling line and activated by electrical signals,
means for activating the exhaust gas recycling valve for diagnosis purposes such that operating parameters of the internal combustion engine change and the reaction of the operating parameters is analysed, wherein when the internal combustion engine is in the idle state and the vehicle driven by the internal combustion engine is stationary, the output signal of an airflow detector located in the inlet tract upstream from the junction with the exhaust gas recycling line is used as the operating parameter.
Furthermore the arrangement can provide:
means for setting the activation signal for the exhaust gas recycling valve to zero based on a value set in the idle state, in order to close the exhaust gas recycling valve,
means for detecting and comparing the signal from the airflow detector with a first threshold value after expiry of a predefined first time period, and
means for concluding that the exhaust gas recycling valve is faulty with regard to dynamic behaviour, if the threshold value is not exceeded within the first time period.
The arrangement can also provide:
means for setting the activation signal for the exhaust gas recycling valve to zero on the basis of a value set in the idle state, in order to close the exhaust gas recycling valve,
means for detecting and comparing the signal from the airflow detector with a second threshold value after expiry of a predefined second time period, and
means for concluding that the exhaust gas recycling valve is faulty with regard to its capacity to close completely, if the threshold value is not exceeded within the second time period.
The invention is characterised by the fact that the exhaust gas recycling valve is closed for checking the exhaust gas recycling valve when the internal combustion engine is in the idle state and the signal from an airflow detector in the inlet tract of the internal combustion engine upstream from the junction of an exhaust gas recycling line with the inlet tract is analysed.
If this signal does not exceed a first predefined threshold value within a first time period, it is concluded that the dynamic of the exhaust gas recycling valve is faulty. If the signal does not exceed a second predefined threshold value within a second time period, it is determined that the exhaust gas recycling valve cannot be completely closed.
When the internal combustion engine is in the speed-controlled idle state, the exhaust gas recycling valve controls the cross-section of the opening of the exhaust gas recycling line generally to a specific position. In this operating state a brief check of the capacity of the exhaust gas recycling valve to be controlled and closed is possible without an adverse effect on drive capacity and drive safety. As the idling of the internal combustion engine is well defined as an operating state and occurs very frequently in day-to-day driving operations (e.g. traffic lights) it is very appropriate for diagnosis purposes. The method in particular has the advantage that no additional sensors are required for checking the capacity of the exhaust gas recycling valve to be controlled and closed.